The proposal is focused on the role of microtubules (MT) in the function and organization of the surface of polymorphonuclear leukocytes (PMN). Alterations of protein and lipid composition of the membrane occur during phagocytosis that are sensitive to colchicine. These changes are hypothesized to occur by a mechanism involving a lateral phase separation within the membrane. This hypothesis will be tested by following the topographic and metabolic fate of phospholipid and other probes inserted into the membrane. Introduction of new membrane components will also be tested. This model is a unique system for the analysis of MT-membrane events. Concanavalin A (Con A) induces the assembly of MT in PMN. Induction of MT by ligands that bind to probes of known orientation within the membrane and by other lectins will be tested by functional (capping) and EM techniques. Alterations in calcium flux that could signal assembly will be studied. The development of MT mediated surface functions during granulocytopoiesis will be studied in normal mouse and man myelocytic leukemia and Chediak-Higashi disease.